The present invention relates to an electromagnetically actuated power transmitting assembly for selective transmission of power to the power driven device from vehicle""s engine system via a pulley driven by an endless flexible driving element, such as a driving belt.
U.S. Pat. No. 5,667,050 discloses an example of a conventional electromagnetic power transmitting assembly. The assembly illustrated in the ""050 patent is of the type that is used with an air conditioning compressor in a motor vehicle. The assembly of the ""050 patent has a pulley structure that rotates on a ball bearing assembly about the input shaft of the compressor. The pulley structure has a grooved outer periphery that engages with a flexible endless belt which is driven by the vehicle""s engine system. The power transmitting assembly of the ""050 patent also has a magnetic coil that induces a field of magnetic flux when energized by electricity supplied from a clutch controller. A ferromagnetic clutch plate is carried by the pulley structure for rotation therewith and an axially movable clutch disc is mounted on the input shaft. The clutch disc is selectively movable in an axial direction between (a) an engaged position wherein the plate and the disc are coupled together to transmit rotation from the rotating pulley structure to the input shaft, thereby supplying power to the compressor, and (b) a disengaged position wherein the clutch disc is de-coupled from the clutch plate to disconnect the pulley structure from the input shaft.
In order to increase or decrease the diameter of the pulley structure in the type of electromagnetic coupling apparatus disclosed in the ""050 patent, there are several methods that can be used. The procedure of decreasing the diameter of the pulley structure without simultaneously decreasing the diameter of the electromagnetic housing must be carried out cautiously with regards to maintaining the limits of adequate thickness within the pulley outer annular portion which includes the grooved surface. The thickness in that portion of the pulley structure is limited by the required structural integrity under the belt load, and the capability to carry the magnetic flux without exceeding the magnetic flux saturation limit. Should the required decrease in diameter of the pulley structure exceed the above mentioned limits then the coil cavity inside diameter (also called a coil hollow or a coil trepan) must also be decreased. Such change involves costly and time consuming changes in production tooling including new coil winding, coil housing and related components.
The procedure of increasing the diameter of the pulley structure by a relatively small increment usually includes the addition of material to the pulley outer periphery. It should be obvious, however, that any increase in the diameter of the pulley outer annular portion without a simultaneous (and costly) increase in the inside diameter of the coil cavity results in greater thickness of the pulley outer annular portion. That, in turn, results in increased inertia and increased production costs.
Furthermore, if the pulley outer diameter must be increased by a large increment and beyond the limits of the thickness range of the pulley outer annular portion, there are at least two prior methods that can be used. One method offers the option to increase the diameter of both the pulley outer periphery as well as the coil cavity. It should be understood that the thickness in the pulley outer annular portion in the type of the pulley structure used in the disclosure of the ""050 patent may be optimized for the required magnetic flux density. In most applications of the type of electromagnetic coupling apparatus disclosed in the ""050 patent the minimum thickness of the pulley outer annular portion required to satisfy the magnetic flux carrying capability is usually sufficient to support the bending and torsional stresses under the driving belt load. Nevertheless, this method of increasing the diameter of the pulley outer periphery while simultaneously increasing the inside diameter of the coil cavity presents the need for a complete re-tooling of the electromagnetic housing assembly including the coil winding, coil housing and the related coil retaining components. This is a relatively very expensive change, also requiring the engineering and manufacturing expertise to accomplish it.
Another option to increase the diameter of the pulley outer periphery by a large increment is to add an annular flux carrier 38 as disclosed in U.S. Pat. No. 4,935,713. This ring-shaped component is usually die-formed into the desirable shape and then attached to the pulley structure by welding. The original inside diameter of the coil cavity is maintained in order to utilize the existing electromagnetic housing and avoid the costly re-tooling. The procedure of increasing the diameter of the pulley outer periphery is then carried out at a nominal cost.
Another similar method of increasing the diameter of the pulley outer periphery by a large increment without simultaneously increasing the inside diameter of the coil cavity and consequently the diameter of the electromagnetic housing is shown in U.S. Pat. No. 5,445,256. This method involves the forming of the magnetic flux frame into a U-shape whereby the original inside diameter of the coil cavity is maintained and the costly re-tooling of the electromagnetic housing is avoided. The procedure of increasing the outer periphery of the pulley structure which is attached to the U-shaped frame by various methods, usually by laser or electron-beam welding, is carried out at a nominal cost.
The arrangements of the ""713 and the ""256 patents, however, still has shortcomings that it would be desirable to eliminate. The main problem with the arrangement of these patents is that the structure responsible for carrying the flux rotates along with the pulley structure and therefore adds to the rotational inertia of the system and detracts from the power transmitting assembly""s overall power transferring efficiency. Further, the rotating flux carrying structures in these patents adds another component to the assembly. This in turn increases component costs and adds extra steps to the manufacturing process.
U.S. Pat. No. 3,455,421 discloses an arrangement wherein a U-shaped metal member is attached to the rear face of the coil and with one leg thereof disposed adjacent the inner diametrical periphery of the pulley""s driven portion. The magnetic flux induced by the coil flows radially through this metal member and through the internal periphery of the driven portion to the face of the pulley structure to affect movement of the clutch member. The pulley structure rotates relative to both the coil and this U-shaped member. Thus, the U-shaped member does not add to the overall rotational inertia of the power transmitting assembly, but does function to bridge the spacing between the coil and the pulley structure""s driven portion.
The power transmitting assembly of the ""421 patent, however, has extra components and requires extra assembly steps both of which it would be desirable to eliminate. In particular, the power transmitting assembly of the ""421 patent has a separate mounting structure that is constructed and arranged to be mounted to the compressor housing and the U-shaped member is formed separately and mounted to that mounting structure.
Consequently, there exists a need in the art for an improved power transmitting assembly in which radial spacing is provided between the magnetic coil and the pulley structure thereof and wherein the radial spacing is effectively bridged to ensure the necessary flow of magnetic flux without unnecessarily adding to the rotational inertia of the power transmitting assembly. Further, it would be desirable to accomplish this with fewer components than used in the prior art arrangements discussed above.
It is an object of the present invention to provide an electromagnetically actuated power transmitting assembly for installation on a power driven device of a motor vehicle to selectively supply power from the vehicle""s engine system to the power driven device via an endless flexible driving element driven by the engine system. The power driven device is of the type having a rotatable input shaft that is selectively rotatable to supply power to the device. The power transmitting assembly comprises a rotatable pulley structure constructed and arranged to be mounted for rotation about the input shaft of the power driven device. The pulley structure provides an annular driven portion constructed and arranged to be engaged with the endless flexible driving element such that engine driven movement of the driving element rotates the pulley structure. The pulley structure comprises ferromagnetic material provided along at least an internal diametrical periphery of the driven portion to allow magnetic flux to flow through the driven portion.
A one-piece flux carrier/mounting structure is formed from ferromagnetic material. The flux carrier/mounting structure comprises an integrally formed mounting structure fixedly mounted to the power driven device and an integrally formed flux carrier portion. An annular magnetic coil is adapted to induce a field of magnetic flux. The coil is fixedly mounted to the mounting structure such that the mounting structure fixedly mounts the coil about the input shaft with the coil spaced radially inwardly from the internal diametrical periphery of the pulley structure driven portion, and the flux carrier portion extending generally radially between the internal diametrical periphery of the pulley structure driven portion and the coil but spaced sufficiently from the internal diametrical periphery to enable the flux field induced by the coil to flow generally radially between the coil and the internal diametrical periphery of the pulley structure driven portion and to allow the pulley structure to rotate relative to both the flux carrier/mounting structure and the coil.
A selectively movable clutch member comprises an attraction portion formed from ferromagnetic material. The clutch member is mounted in power transmitting relation to the input shaft such that rotating the clutch member rotates the input shaft to supply power to the power driven device. The clutch member is positioned such that the magnetic flux flowing through the bridge portion to the flux carrying portion magnetically attracts the attraction portion of the clutch member to selectively move the clutch member between a disengaged position wherein the clutch member de-couples the pulley structure from the input shaft to allow the pulley structure to rotate relative to the input shaft and an engaged position wherein the clutch member couples the pulley structure and the input shaft so that rotation of the pulley structure under engine driven movement of the endless flexible driving element rotates the clutch member, which in turn rotates the input shaft device to thereby supply power to the power driven device.
Another aspect of the present invention provides a method for making a plurality of pulley assemblies of the type described above. This method comprises:
providing a coil inventory of the stationary annular magnetic coils, each of the coils of the coil inventory being substantially identical;
providing a first pulley structure inventory of first pulley structures, the annular driven portions of the first pulley structures each having a first outer diameter at a driving element engaging surface thereof and a first inner diameter at the inner diametrical periphery thereof;
providing a second pulley structure inventory of second pulley structures, the annular driven portions of the second pulley structures each having a second outer diameter at a driving element engaging surface thereof different from the first outer diameter and a second inner diameter at the inner diametrical periphery thereof different from the first inner diameter;
providing a first flux carrier/mounting structure inventory of first stationary one-piece flux carrier/mounting structures each formed from ferromagnetic material, the first flux carrier/mounting structures each comprising an integrally formed mounting portion constructed and arranged to be fixedly mounted to the power driven device and an integrally formed flux carrier portion having a first radial extent selected to extend generally radially between the internal diametrical periphery of the annular driven portion of an associated first pulley structure and an associated coil to enable the flux field induced by the associated coil to flow generally radially between the associated coil and the internal diametrical periphery of the driven portion of the associated first pulley structure and to allow the associated first pulley structure to rotate relative to both its associated first flux carrier/mounting structure and the associated coil;
providing a second flux carrier/mounting structure inventory of second stationary one-piece flux carrier/mounting structures each formed from ferromagnetic material, the second flux carrier/mounting structures each comprising a mounting portion constructed and arranged to be fixedly mounted to the power driven device and a flux carrier portion having a second radial extent selected to extend generally radially between the internal diametrical periphery of the annular driven portion of an associated second pulley structure and an associated coil to enable the flux field induced by the associated coil to flow generally radially between the associated coil and the internal diametrical periphery of the driven portion of the associated second pulley structure to rotate relative to both its associated second flux carrier/mounting structure and the associated coil;
providing a clutch member inventory of selectively movable clutch members;
fixedly mounting a coil from the coil inventory to a first flux carrier/mounting structure from the first flux carrier/mounting structure inventory;
assembling a first power transmitting assembly package including a first pulley structure from the first pulley structure inventory, the first one-piece flux carrier/mounting structure with the coil from the coil inventory fixedly mounted thereto, and a selectively movable clutch member from the clutch member inventory;
delivering the first power transmitting assembly package;
mounting a coil from the coil inventory to a second flux carrier/mounting structure from the second flux carrier/mounting structure inventory;
assembling a second power transmitting assembly package including a second pulley structure from the second pulley structure inventory, the second one-piece flux carrier/mounting structure from the second flux carrier/mounting structure inventory with the coil from the coil inventory fixedly mounted thereto, and a selectively movable clutch member from the clutch member inventory;
delivering the second power transmitting assembly package.
In accordance with this method, pulley assemblies having pulley structures with driven portions of varying outer and inner diameters can be made using a single inventory of substantially identical magnetic coils.
Other objects, features, and advantages of the present invention will become apparent from the following detailed description, the accompanying drawings, and the appended claims.